Our goal is the development of methods for the chemical synthesis of proteins. Toward this end, we intend to study peptide segment coupling. Peptides will be prepared by the solid-phase method and coupled together by two alternative strategies: (a) deprotected peptides will be coupled in aqueous solution; (b) protected peptides will be coupled on the solid phase in non-aqueous medium. By the "aqueous" strategy, work with water soluble peptides will allow us to take advantage of the powerful methods of purification in peptide/protein chemistry: ion-exchange chromatography, partition chromatography, etc. We have previously shown that a peptide containing a C-terminal thiolcarboxyl group can be specifically coupled to an amine peptide in water by activation with silver nitrate, without interference by free carboxyl groups. In the "non-aqueous" strategy the full convenience of the solid-phase method will be exploited by coupling protected peptides with a C-terminal thiolcarboxyl group onto the solid-phase to give proteins. Synthetic methodology developed here will be applied to the synthesis of hormonal polypeptides such as human beta-lipotropin and human somatotropin. The aqueous strategy also has the possibility of application to the specific conjugation of peptides (as large as fifty amino acids) to proteins for biological and immunological studies, and to protein semisynthesis. Ultimately we intend to take a synthetic approach toward the understanding of the mechanism of action of protein hormones.